Composite compact components fabricated with high temperature brazing filler metal and method for making same

ABSTRACT

A component comprised of a composite compact, preferably diamond, and a substrate bonded to the compact. A preferred embodiment of the component is a cutter for a drill bit. The compact is comprised of a layer of bonded diamond or boron nitride particles and a base layer of cemented carbide bonded, preferably under high temperatures and pressures, to the particulate layer. The particulate layer is degradable by exposure to temperatures above a predetermined temperature. The substrate is bonded to the base layer of the compact with a filler metal which, to form a bond, requires the exposure of the surfaces to be bonded to a temperature substantially greater than the degradation temperature of the particulate layer. The component is fabricated by heating the base layer, filler metal and substrate to a temperature in excess of the degradation temperature while maintaining the temperature of the particulate layer below the degradation temperature via a heat sink.

CROSS REFERENCE TO RELATED APPLICATIONS

U.S. Pat. application Ser. No. 699,411; filed June 24, 1976, now U.S.Pat. No. 4,109,737 and assigned to the assignee of the invention hereinis directed to a rotary drill bit comprising a plurality of cuttingelements, each of which is comprised of an elongated pin with a thinlayer of diamond bonded to the exposed end of the pin. The pin ismounted by press fitting into the drill crown.

U.S. Pat. No. 4,098,362 is directed to a rotary drill bit comprising aplurality of diamond compact cutters. The diamond compact cutters aremounted in a drill crown by molding or by attachment to a cementedcarbide pin which is in turn mounted in a drill crown by pressedfitting. Brazing is also disclosed as an alternate technique formounting such compact cutters in the drill crown.

U.S. Pat. No. 4,156,329 is directed to a method for fabricating a drillbit comprising a plurality of composite compact cutters by furnacebrazing each cutter in a recess in the crown of the drill bit. In oneembodiment each cutter is comprised solely of a composite compact with alayer of brazing filler metal coating the exposed surface of thesubstrate of the compact. In another embodiment each cutter is comprisedof a composite compact bonded to one end of a cemented carbide pin, theother end of which is fixed in a recess of the drill bit crown.

BACKGROUND OF THE INVENTION

This invention relates to components comprised of abrasive compacts.Typical areas of application for such components are in wire dies, wearsurfaces, rock cutting and drilling equipment and cutting tools formachining. The area of primary interest for this invention is incomponents useful as cutters for rock drilling bits and techniques forfabrications of such components.

A cluster compact is defined as a cluster of abrasive particles bondedtogether either (1) in a self-bonded relationship, (2) a means of abonding medium disposed between the crystals, or (3) by means of somecombination of (1) and (2). Reference can be made to U.S. Pat. No.3,136,614, U.S. Pat. No. 3,233,988 and U.S. Pat. No. 3,690,818 for adetailed disclosure of certain types of compacts and methods for makingsame. (The disclosures of these patents are hereby incorporated byreference herein.)

A composite compact is defined as a cluster compact bonded to asubstrate material such as cemented tungsten carbide. A bond to thesubstrate can be formed either during or subsequent to the formation ofthe cluster compact. Reference can be made to U.S. Pat. Nos. 3,743,489,3,745,623 and 3,767,371 for a detailed disclosure of certain types ofcomposite compacts and methods for making same. (The disclosure of thesepatents are hereby incorporated by reference herein.)

Brazing is defined as a group of welding processes wherein coalescenseis produced by heating to suitable temperatures above 800° F. and byusing a brazing filler metal having a melting point below that of thebase metals. The filler metal is distributed between the closely fittedsurfaces of the joint by capillary action.

Filler metal is defined as brazing filler metals and other metals oralloys used in bonding techniques such as diffusion bonding, hotpressing, resistance welding and the like. The filler may be eitheradded as an additional component to the metal parts being bonded orformed from the metals of the parts themselves (e.g., fusion welding asdefined in Van Nostrand's Scientific Encyclopedia, Fifth Edition (1976)pp 2330-2331).

A brazing filler metal is defined as a metal or alloy to be added whenmaking a braze and having melting temperature above 800° F. (but belowthose of the metals being joined).

Conventional rotary drill bits for oil and gas well drilling and coredrilling have heretofore used cutting elements such as (1) steel teeth,(2) steel teeth laminated with tungsten carbide, (3) an insert ofcemented tungsten carbide, and (4) natural diamonds, all of which areset or molded in a tungsten carbide crown or cone. Due to the relativelyshort life and/or high operating cost of these conventional designs, ithas recently been proposed to use synthetic diamond composite compactsas the cutting element in such drills.

In adapting composite compacts to certain drill bit applications, it hasbeen found to be desirable to provide an elongated base or support forthe composite compact to aid in attachment in the drill crown. While itis technically feasible to form an integral composite compact of anadequate length directly under high temperature and pressure, asdisclosed in application Ser. No. 699,411 cross referenced above, thishas not as yet been adopted commercially because of the significantlyincreased cost of manufacture. This becomes clear when realizing thatthe capacity of the reaction cell in which the compacts are made, underhigh temperatures and pressures, is limited. Thus, if compacts wereproduced as suggested in application Ser. No. 699,411, the number ofcompacts produced per cell would be reduced by about one-halfpotentially making the cost prohibitive.

One approach to avoiding this added cost is to braze an additionallength of cemented carbide to the carbide base of the composite compactas disclosed in application Ser. Nos. 746,044 and 796,635 crossreferenced above.

In field tests of these latter two designs, one problem which has beenencountered is that the stresses on each cutting element are severe andsome disattachment of the cutters has been encountered. The stresses arecaused because the structure of most rocks is heterogeneous and thushave layers of varying hardness. These layers cause large variations inthe impact loads applied to the cutting elements during drilling, andthe bond strength of such designs is not always strong enough towithstand this.

In these designs, available attachment techniques and acceptable brazingfiller metals for use with a diamond composite compact made inaccordance with the teaching of U.S. Pat. No. 3,745,623 were limitedbecause the diamond layer of such compacts is thermally degraded attemperatures above approximately 700° C. Similarly, it has been foundthat a cubic boron nitride (CBN) composite compact made in accordancewith the teaching of U.S. Pat. No. 3,743,489 is also thermally degradedat temperatures above approximately 700° C. Because of the thermaldegradation problem, it has been necessary to use brazing filler metalswith a liquidus below 700° C. Such metals form brazing joints generallyof lower strength than braze filler metals having a higher liquidus.Even when the lower temperature liquidus metals (such as BAg-1-ASW-ASTMclassification) are used, temperatures approaching those at which thediamond layer is degraded are required; hence, great care is required toprevent degradation of the compact during brazing.

Accordingly, it is an object of this invention to provide improved andstronger components comprised of composite compacts.

Another object of this invention is to provide an improved cuttercomponent for drill bits.

Another object of this invention is to provide an improved fabricationtechnique for forming high strength bonds to composite compacts withoutdegrading the particulate layer of the composite compact.

Another object of this invention is to provide an improved fabricationtechnique for forming a high strength bond between a composite compactand cemented carbide pin in the fabrication of cutters for drill bits.

Another object of this invention is to provide improved techniqueswhereby small composite compacts produced by an expensive hightemperature, high pressure process can be dimensionally scaled up tolarger sizes permitting easier attachment of the compact to a tool body.

SUMMARY OF THE INVENTION

These and other objects of the invention are accomplished by a componentcomprised of a composite compact bonded to a substrate with a hightemperature filler metal which, to form a bond, requires the exposure ofthe surfaces to be bonded to a temperature substantially greater thanthe degradation temperature of a particulate layer of the compact and amethod for fabrication thereof. The method comprises the steps of (1)disposing the composite compact in thermal contact with a heat sink, (2)disposing the compact adjacent to a substrate with a high temperaturefiller metal disposed therebetween, and (3) heating the base layer ofthe compact, filler metal and substrate to a temperature in excess ofthe degradation temperature to form a high strength bond whilemaintaining the temperature of the particulate layer of the compactbelow the degradation temperature thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary perspective view of a component in accordancewith the features of this invention.

FIG. 2 is a schematic diagram of an apparatus for fabricating acomponent in accordance with the features of this invention.

FIG. 3 is an enlarged plan view of a central portion of the apparatusshown in FIG. 2.

FIG. 4 is a view taken along line 4--4 of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a component 11 in accordance with one embodiment of theinvention. Component 11 is comprised of (a) a composite compact 13, (b)a pin or substrate 15, and (c) a thin, continuous layer 17 of fillermetal (shown disproportionately large for purposes of illustration)disposed between and bonding substrate 15 to compact 13 along aninterface 16. The component configuration may, of course, be widelyvaried to suit the particular application.

Composite compact 13 is comprised of a particulate mass or layer 19 ofbonded abrasive particles of either diamond or hard phase boron nitrideand a mass or base layer 21 of cemented carbide bonded to compact 13along an interface 23. Carbide mass 21 is also provided with an exposedsurface 25 remotely spaced from interface 23.

In a preferred embodiment of compact 13, as explained in detail in U.S.Pat. No. 3,745,623, layer 19 is comprised by volume of at least 70%diamond and preferably in excess of 90% diamond. The remaining 30% orless is primarily comprised of the bonding material, preferably cobalt(or alloys), of the cemented carbide mass 21 which is infiltrated intolayer 19 during the high temperature, high pressure fabrication process.

In an alternative embodiment of compact 13, compact 13 may be comprisedof a hard phase boron nitride layer 19 constructed in accordance withU.S. Pat. No. 3,743,489 or U.S. Pat. No. 3,767,371 (incorporated byreference herein). The hard phase boron nitride may be either of a cubicor hexagonal structure. The referenced patents disclose only the use ofthe cubic form, however, the hexagonal form may be substituted in wholeor in part for the cubic form.

Substrate 15 is preferably comprised of cemented carbide preferably thesame as carbide mass 21. See U.S. Pat. No. 3,745,623; col. 5, line 58 tocol. 6, line 9, for a detailed description of acceptable types ofcemented carbide. Cemented carbide is preferable, particularly in drillbit applications, because of its hardness and impact resistance.Alternatively, masses 15, 21 may be composed of a ceramic, such asalumina, elemental metal or an alloy depending upon the particularcharacteristics required by the application for which the component isto be used. Reference can be made to U.S. Pat. No. 3,982,911 for adetailed description of acceptable materials. This patent is herebyincorporated by reference herein.

Filler metal 17 is preferably a high temperature, high strength brazingfiller metal having a liquidus greater than the degradation temperatureof particulate mass 19. As stated above in the case of a diamond andboron nitride composite compact made in accordance with U.S. Pat. No.3,743,489 and U.S. Pat. No. 3,745,623 respectively, the degradationtemperature is about 700° C. Acceptable filler metals may be selectedfrom the group of alloys compatible with the materials being brazed. Theability to use such high strength brazing filler metals in accordancewith this invention enables the formation of a strong bond betweencompact 13 and substrate 15. For example, bonds with a torsional shearstrength of 6.5×10⁸ to 3.4×10⁸ n/m² measured over a temperature range of25° C. to 350° C. respectively have been achieved by brazing with abraze alloy commercially identified as Anaconda 773 brazed at about 950°C. for a component as shown in FIG. 1. In this test, base 21 and pin 15were Co cemented WC. This may be compared to torsional shear strength of4.0×10⁸ to 1.2×10⁸ n/m² measured over a temperature range of 25° C. to350° C. respectively, for a component as in FIG. 1 except that the bondconsisted of brazing filler metal BAg-1 (ASW-ASTM classification) (whichis a Ag alloy).

As defined above, filler metal 17 may be alternatively a metal or alloyused in bonding techniques such as diffusion bonding, hot pressing,resistance welding and the like.

FIGS. 2-4 show an apparatus 51 for fabricating component 11 shown inFIG. 1 by brazing in accordance with a preferred embodiment of themethod of this invention. Apparatus 51 (FIG. 2) is comprised of a framemember 52. Fixed to frame 52 are a pair of pneumatic cylinders 53, 55for holding, relative to an induction coil assembly 58, a component 11for brazing. The pneumatic cylinder 53 (FIGS. 2, 3) comprises a plunger59 with a recessed head 61 for receiving one end of composite compact13. Head 61 is provided with a coolant, preferably water, via tube 65from a coolant supply 67 of a conventional construction. Head 61 andcoolant supply 67 together function as a heat sink for diamond layer 19during the brazing of compact 13 to substrate (pin) 15.

Pneumatic cylinder 55 is similarly comprised of a plunger 69 with a head71 fixed at one end thereof. A cup-shaped ceramic insulator 78 ispositioned on head 71 for supporting one end of a substrate preventingthe heat sinking of pin 15 to head 71 during brazing. Head 71 is alsointerconnected to coolant supply 67 via tube 65.

Pneumatic cylinders 53, 55 (FIG. 2) are supplied air under pressure fromair supply 66 through control valves 77, 79 respectively. When extended,(FIGS. 2, 3) plungers 59, 69 position component 11 coaxially ofinduction assembly coil 58 which is supported on frame 53 by supports83, 85. (A third support for assembly 58 is not shown.)

FIG. 4 shows an enlarged plan view of assembly 58 taken along line 4--4of FIG. 3. Coil assembly 58 is of a conventional and well-knownconstruction and is available commercially from Lepel High FrequencyLaboratory, Inc.; New York, N.Y. Coil assembly 58 is comprised of acoiled electrically conductive (Cu) tube 87 and a Cu plate 91. Plate 91and coiled tube 87 are held together by a plurality of clamps 90. Theintermost coil 89 of tube 87 is fixed and electrically connected tocopper plate 91 and the remaining coils are electrically insulated fromplate 91 via insulator 92. Tube 87 of induction coil 81 isinterconnected to an RF generator 93 for energizing assembly 58. As iswell known, assembly 58 when energized, generates a highly localizedmagnetic field in the region about the intersection of the plane ofassembly 58 and the axis perpendicular to the plane and passing throughthe center of coiled tube 87. This field induces electric current in aconductive member disposed axially of assembly 58 and will directlyprovide only localized heating of support 15 in the region of themagnetic field generated by assembly 58.

It is preferred to position component 11 (unbrazed condition) withinterface 17 located about 3 mm above the plane of assembly 58. Thisallows heat to spread conductively from the inductively heated area tointerface 17.

It has been found surprisingly that high strength bonds may be formed tocompact 13 in this manner without degradation of layer 19. The abilityto elevate the interface 16 to a temperature far above the degradationtemperature of layer 19 while maintaining layer 19 below its degradationtemperature is believed to be due at least in part to the mismatchedthermal conductivities of layer 19 and mass 21. For example, in acommercial embodiment constructed by the teaching of U.S. Pat. No.3,745,623 layer 19 has a thermal conductivity approximating that ofsingle crystal which is about 5.9 cal/(sec)(°C.)(cm) while the carbidelayer has a thermal conductivity of about 0.25 cal/(sec)(°C.)(cm). Thispermits the interface to reach a much higher temperature than the layer19 as heat may be conducted away rapidly from layer 19 by heat sinkingin accordance with this invention.

A preferred embodiment of the method for practicing this invention withapparatus 51 is set forth below. A substrate 15 is placed in a ceramiccup 78 and together disposed on head 71. Head 71 is then actuated intoits extended position via air valve 79. A conductive paste is applied todiamond layer 19 of composite compact 13 after which the compositecompact is positioned in recess 101 of head 61. The paste bonds compact13 to head 61 and provides a good thermally conductive path therebetweenfor heat sinking layer 19. A silver or other conventional paste materialcan be used to establish a good thermal path between layer 19 and head61. Air valve 77 is then actuated to position compact 63 in firmengagement with substrate 75 with a quantity of filler metal 17 providedat the interface of compact 13 and pin 15. Engagement pressures between2.1×10³ n/m² and 8.3×10⁴ n/m² are acceptable. RF generator 93 is thenactuated for approximately 6 to 30 seconds to heat filler metal 17 to amolten condition and thereby firmly bond compact 13 to pin 15. The upperlimit of time is not critical when layer 19 is properly cooled.Generator 93 is then deactivated. Following this, valves 77, 79 aredeactivated to retract plungers 59, 69 to permit removal of thecompleted component 11.

A substrate 15 is preferably prepared for brazing by applying a thinlayer of a brazing filler metal directly to one end thereof. The layeris then ground or polished to a thickness of 0.12 mm preferably.Alternatively, it will be recognized by those skilled in the art that ashim or powder mixture of brazing filler metal and flux may bepositioned between composite compact 13 and substrate 15 as substrate 15and compact 13 are positioned between plungers 59, 69.

Accordingly, while the invention has been shown and described inconnection with certain preferred embodiments thereof, other embodimentsand modifications will be apparent to those skilled in the art. Forexample, the preferred method of heat sinking layer 19 is by use of awater cooled head 61 of steel. However, other materials may be used forhead 61 as well as other coolants or coolant techniques. Also techniquessuch as laser, electron beam, arc plasma, and resistance interfaceheating for localized heating of substrate 15 to the brazing temperaturemay be used. Still further, the ability to retain the particulate layerbelow its degradation temperature while exposing the surfaces to bebonded to temperatures exceeding the degradation temperature of thelayer permits the use of other conventional high temperature bondingtechniques such as diffusion bonding, hot pressing, resistance weldingand the like in accordance with the features of this invention. It isintended that the appended claims cover all such embodiments andmodifications as are within the true spirit and scope of this invention.

I claim:
 1. An improved component of the type comprised of:A. anabrasive composite compact made of a layer of bonded abrasive particlesselected from the group consisting of diamond and cubic boron nitridebonded together, said layer being bonded to a base layer made of amaterial selected from the group consisting of cemented metal carbideselected from the group consisting of tungsten carbide, titanium carbideand tantalum carbide wherein the material providing the metal bond isselected from the group consisting of cobalt, nickel, iron and mixturesthereof; an elemental metal which forms a stable nitride or boride; anda metal alloy which forms a stable nitride or boride; B. which compositecompact is bonded to a substrate made of a material selected from thesame group used for the base layer; C. by a layer of brazing fillermetal disposed between said abrasive compact and said substrate;wherein, the improvement comprises those components in which the brazingfiller metal has a liquidus substantially above 700° C. and the thermaldegradation temperature of the layer of bonded abrasive particles. 2.The improved component of claim 1 wherein both the base layer and thesubstrate are made of a metal bonded carbide selected from the groupconsisting of tungsten carbide, titanium carbide and tantalum carbidewherein the metal providing the metal bond is selected from the groupconsisting of cobalt, nickel, iron and mixtures thereof.
 3. The improvedcomponent of claim 2 wherein the abrasive particles are made fromdiamond, and wherein the base layer and substrate are both made from thesame type of cemented carbide.
 4. In a method for fabricating acomponent comprised of:A. an abrasive composite compact made of a layerof bonded abrasive particles selected from the group consisting ofdiamond and cubic boron nitride bonded together, said layer being bondedto a base layer made of a material selected from the group consisting ofcemented metal carbide selected from the group consisting of tungstencarbide, titanium carbide and tantalum carbide wherein the materialproviding the metal bond is selected from the group consisting ofcobalt, nickel, iron and mixtures thereof; an elemental metal whichforms a stable nitride or boride; and a metal alloy which forms a stablenitride or boride; B. bonded to a substrate made of a material selectedfrom the same group used for the base layer; C. by a layer of brazingfiller metal which method comprises brazing said abrasive compact tosaid substrate using a brazing filler metal the improvement whichcomprises:(i) using a brazing filler metal having a liquidussubstantially greater than 700° C. and the thermal degradationtemperature of the abrasive; and (ii) disposing the abrasive compositecompact in thermal contact with a heat sink during the brazingoperation.
 5. The improved method as recited in claim 4 wherein both thebase layer and the substrate are made from a metal bonded carbideselected from the group consisting of tungsten carbide, titanium carbideand tantalum carbide wherein the metal providing the metal bond isselected from the group consisting of cobalt, nickel, iron and mixturesthereof.
 6. The improved method as recited in claim 5 wherein thebrazing temperature is about 950° C.
 7. The improved method of claim 4which further comprises the step of providing a coating of a highthermally conductive material between said layer of bonded abrasiveparticles and said heat sink to establish a highly thermally conductivepath therebetween and wherein in step (ii) the layer of bonded abrasiveparticles is disposed in a recess in said heat sink.